Recently, in dental surgery, orthodepic surgery, otorhinolaryngology and the like, artificial bone-supplying materials have been used to supply a lost part of bone due to the fracture of bone, a bone tumor, and pyorrhea alveolaris. Of these artificial bone-supplying materials, a calcium phosphate-based material exemplified by hydroxyapatite has received the greatest attention as an excellent bone-supplying material because of its high affinity to a living body. In addition to having good affinity to a living body, an artificial bone-supplying material is required to have a sufficiently high strength.
The calcium phosphate-based material used in the applications described above has heretofore been produced by press molding a calcium phosphate powder by techniques such as hot pressing (HP) and hot isostatic pressing (HIP) while at the same time heating, or press molding it by techniques such as cold isostatic pressing (CIP), and then firing the resulting molding at a temperature of about 1,000.degree. C. In the calcium phosphate-based material thus obtained, as the relative density (where the density calculated with the density of a calcium phosphate-based material not containing any air bubbles is 100%) is higher, the strength generally tends to be higher.
In the method comprising heating simultaneously with press molding by techniques such as hot pressing (HP) and hot isostatic pressing (HIP), the strength can be increased by increasing the relative density. This method, however, has a problem in that large-scaled equipment is needed, leading to a marked increase in the production cost.
In the method comprising press molding by techniques such as cold isostatic pressing (CIP) and then firing, the relative density can be increased to a certain extent by increasing the firing temperature. In this method, however, a problem arises in that the calcium phosphate-based material starts to decompose at a firing temperature exceeding about 1,400.degree. C., because the melting point of e.g., hydroxyapatite is about 1,650.degree. C. For this reason, increasing the firing temperature is limited, and thus the ability to increase the relative density by raising the firing temperature is also limited.
Moreover, although the relative density can also be increased to a certain extent by raising the firing temperature, if the firing temperature is raised, the primary particles of the sintered body tend to become large. Thus, a problem arises in that the strength is not increased in proportion to an increase in the relative density.